Apparatus for separating particulate materials



April 14, 1942.- M, E, HAWORTH 2,279,590

APPARATUS FOR SEPARATING PARTICULATE MATERIALS Filed Feb. 6, 1939 5Sheets-Sheet l April 14, 1942. M. E. HAWORTH APPARATUS FOR SEPAI YATINGPARTICULATE MATERIALS Filed Feb. 6, 1939 5 Sheets-Sheet 2llllllllllllllllllllll l H nufln l hul l l hul l l mlml w llw INVENTOR.

A; ATTORNEYS,

loobo Apnl 14, 1942. M. E. HAWORTH 2,279,590

APPARATUS FOR SEPARATING PARTICULATE MATERIALS Filed Feb. 6, 1959 5Sheets-Sheet 4 TERMIN AL VELOCITY IN FEET PE R MINUTE N n I om- N n Qnmwm- N s Q h wm O 0 0 0 0009009 Q 0 000000 3 0 u ooc qoo- DIAMETER 0FPARTICLES IN INCHES M ATTORNEYS.

April 14, 1942. M. E. HAWORTH APPARATUS FOR SEPARATING PARTICULATEMATERIALS Filed Feb. 6, 1939 5 Sheets- Sheet 5 loooo 9000 8000 7000 000o o 0 0 o o 0 o 0 0 o o o o 0 0' 0 o 0 o O o 0 000000 a o 0 098 65 4 3 2I 0 o 086 7 6 5 4 3 2 I v Q Q P- Q mo 3 so no no 2. me

3 v HSE E GE num 233 C.G3- E FEES. @533 DIAMETER OF COARSEST PARTICLES1N BED INCHES.

INVENTOR BY 1 mow W fi/lM/MwvxflLe/ 44 ATTORNEYS.

Patented Apr. 14, 1942 STATES PATENT orF cE APPARATUS FOR SEPARATINGPARTICU-' LATE MATERIALS Mack E. Haworth, Pittsburgh, Pa., assignor toRoberts and Schaefer' Company, Chicago, 111., a corporation of IllinoisApplication February 6, 1939, Serial No. 254,750

UNETED Claims. ,(531. 209-466) This invention relates to the separatingor cleaning of particulate materials in which light, intermediate andheavy density particles are mixed together, the separations beingeffected principally by a process in which the laws governing hinderedand crowded settling fundamentals prevail. For the purpose ofillustration only, raw coal, by which is meant a mixture of pure coalandheavier density impurities or foreign matter encountered in mining,such as bone coal, shale and pyrites, will be used as an example of suchparticulate material. A dry cleaning process using air as the fluidmedium will serve as a basis for illustrating the method employed.

Many types of apparatus have been designed for this general purpose, andsome have met with a certain degree of success, but in so far as I know,all of them have failed to accomplish the desired degree of refinementin the separations or cleaning. That is, after cleaning, a certainpercentage of heavier density particles remains mixed with the lightdensity particles, i. e., clean or pure coal, and an unduly large amountof coal remains mixed with the removed intermediate and heavy densityparticles, known as the rejects or foreign matter. As long as thissituation prevails either the coal is not properly cleaned, or coal iswasted with the rejects, or both.

In the dry cleaning of coal as generally practiced heretofore, the rawcoal is fed in a continuous stream to one end of an inclined table ordeck which may be reciprocated to agitate the raw coal and cause it totravel toward the opposite end of the deck. The deck is perforated orforaminous to permit fiuid under pressure to be forced upwardly throughthe mixture of raw coal. If the bed is mechanically agitated, this fiuidis usually continuously moving air delivered to the deck at a velocitysuflicient to loosen up the mixture and thereby facilitateStratification; In case the deck is stationary, a pulsating air currentis used for agitating the mixture.

Heavy density particles settle' through the mixture and produce a bed ofsuch particles on the pervious deck surface. This bed is made up ofpyrites, shales, and coarser heavy bone coal, and its density istherefore high compared with the coal and lighter bone particles. Theterm bone coa designates the fractions containing a high percentage ofcombustible material, but containing too much ash or sulphur to beincluded with the clean coal; and includes the fractions from theheaviest coal particle permissible in the clean coal to about 1.90specific gravity. It will be understood that laminated particles such ascoal and shale; bone and shale; coal, pyrite, bone and shale, or variouscombinations thereof, having a specific gravity included Within thespecific gravity range specified, are

- included under this term. The term shale or slate designates thefractions from about 1.90 specific gravity to about 2.60 specificgravity and includes shale, varying in density from 2.30 to 2.60,together with laminated particles of coal, bone, pyrite and shale invarious combinations in which the particles have specific gravitieswithin the specific gravity limits specified for this term.

The term pyrites designates the fractions from about 2.60 specificgravity to about 4.80 specific gravity and includes laminated particlesof coal;

bone, shale and pyrite in Various combination 'in which the particleshave specific gravities within the specific gravity limits specified forthis term.

It is characteristic of crowded settling stratification, which takesplace in the 'heavy density bed, that small heavy density particles thatreach the lower-strata wedge their way under larger ones'and form thebottom of the heavy densitybed which acts in a manner similar to a heavydensity fluid and crowds out or prevent's'lighter particles frompenetrating it.

Above the heavy density bed are foundthe in termediate and light densitybone particles, fine heavy density particles, and coal particles whichextend to the top of the raw coal mixture. The light density particles,i. e., pure coal, preponderate in the upper bed. The term pure coal?des-f ignates the lighter specific gravity fractions in the mixture ofraw coal, and ordinarily includes the fractions from about 1.25 specificgravity'jto a range between 1.40 and 1.50 specific gravity or slightlywider, depending upon the specific gravity of the heaviest density coalparticles permissible in the clean coal product.

In order to satisfactorily separate the light density coal particlescontained in the upper bed from the heavy density particles in the loweror heavy density bed, the intermediate bed which comprises both coal andforeign particles and is known as middling is withdrawn separately fromthe side or end of the body of raw coal.- However, there is too muchcoal in this intermediate bed for efiicient cleaning. Ordinarily thesemiddlings are recirculated and the heavier density particles removed asrejects or subjected to retreatment for recovery of coal particlescontained therein. If the middlings, or the middlings and rejects, areretreated by a similar T process in similar apparatus, some recovery ofthe light density coal particles therein may be obtained, but thattreatment is characterized by the same overlap of size-density rangewhich characterizes the primary treatment. Therefore, eflicientseparations have not been obtained with the systems used heretofore, anddry cleaning has not proved successful at all with raw coal mixtures inwhich the particles are maller than A; inch in diameter.

It is among the objects of this invention to provide a method andapparatus for separating or cleaning particulate materials which ishighly efl'icient, relatively inexpensive, suitable for materialcomprising very small sizes, and readily adaptable to materials ofdifferent character.

My invention is predicated'in part upon my discovery that in order toproduce proper stratification in separations by a dry cleaning processthe settling or terminal velocities of the particles must bear adefinite relation to the upward fluid current through a mixture of them.The terminal velocity of a particle is the velocity at which it fallsfreely through a fluid medium after the resistance of the fluid hasstopped acceleration of the particle's velocity. That is, if a certainparticle has a terminal velocity of 1000 feet per minute in still air,the particle will teeter in an upward air stream having approximatelythat velocity. Terminal velocities depend not only on the specificgravity or density of the particles, but also upon their size and toalesser extent their shape. Consequently, certain small size heavydensity particles settle at the same rate, or have the same terminalvelocities, as

larger lighter density particles so that certain particles tend toassociate together in their falling.

Due to restriction of the upward air current by the raw coal, thevelocity of the air as it passes through'the voids between the particlesin the mixture is greatly increased. I use air at-a velocity thatproduces a fluid or mobile condition of the bed of coal in order toobtain hindered settling and rapid Stratification. That is, the aircurrent causes the coal bed actually to expand upwardly so that the coalparticles appear almost to be floating in the bed. It is unnecessary andmay even be undesirable, to develop mobility of the intermediate andheavy density beds in which crowded settling occurs. The largest heavydensity particles, which are foreign particlescomprising pyrites,shales, heavy bone, and the like, settle rapidly through the upward aircurrent because their terminal velocities are materially greater thanthe velocity of the air that would normally be used. Any particles thathave terminal velocities less than the velocity of the air passingthrough the mixture can not settle therein, although they will not becarried away with the air unless their terminal velocities, are alsoless than the air velocity above the mixture where it again assumessubstantially the same velocity it had below the deck.

It is therefore important that, before stratification is attempted, theparticles of raw coal be sized by screening or other means in order toproduce a mixture in which substantially'all of the foreign particlesthat it is desired to, remove have terminal velocities greater than theminimum air velocity upwardly through the mixture that it Will benecessary to use to keep the lightest density bed- (coal) thereinexpanded or mo-, bile during final stratification. This presizing factorhas never before been recognized, so far as I know. In the case of verysmall particles, such as those passing through a V inch square sists ofsubstantially pure coal.

mesh screen, the presizing should be preceded by an effective drying anddedusting operation; otherwise, presizing is very difficult, if notimpossible.

Furthermore, in accordance with this invention, cleaning is notattempted with only one deck, but the raw coal passes from one toanother of a series of independent short decks from each of which someof the foreign particles are removed until the overflow from the lastdeck con- To prevent as much as possible the mixing of coal with therejects, the rejects are withdrawn from each deck through an opening inits bottom, and a bed of the heavier density particles remaining ismaintained' at all times above the draw so as to prevent to the greatestpossible extent the lighter density coal particles from reaching it. The

maintenance of such a lower bed of suitable thickness depends to a largeextent upon the rate of travel of particles across the deck. With auniform rate of deck reciprocation or oscillation, a uniform stroke, andgiven rates of feed and withdrawal of particles, I have found that thelongitudinal inclination or pitch of each deck determines the rate oftravel across the deck and, consequently, whether the lower bed will bedeveloped; whether, if developed, it will move toward the draw tooslowly, and thus limit the rate at which it may be withdrawn; or whetherit will move too rapidly and thus be dissipated, any one of whichconditions will prevent proper stratification or separation. The pitchof each deck is therefore made adjustable so that the lower bed will bemaintained of substantially constant thickness. The pitch of each deckis independently adjustable and the supply of air to each is likewiseseparately controlled because the characteristics of the mixture of rawcoal on each deck are different, due to the removal of certain foreignparticles from the preceding deck.

As the density range of the particles in the raw coal becomes narrowerbecause of the removal of the heavier density particles through thepreceding decks, there will eventually be some mixing of coal particleswith the intermediate density particles then drawn off. This mixing isdue to the lower bed no longer being dense enough to prevent some of thecoal particles from penetrating it and filling up the voids not filledby particles other than coal. In other words, the type of stratificationexisting in the lower bed is no longer the crowded settling typeexisting in the lower bed of the first deck, but more nearly approachesthe hindered settling type existing in the upper bed. The averagedensity of the particles in the lower bed a;- proaches the averagedensity of the coal particles. In order to recover the coal thuswithdrawn with the intermediate density rejects, a process is employedin which the separation is effected by density only and in which sizeand shape have no influence. Such a process is one in which a fluid isemployed at the gravity required to effect the desired separation and iscommonly referred to as a heavy density fluid process. If desired, theparticles recovered from the last draw may be recirculated over all ofthe decks in order to build up denser lower beds that will moresuccessfully resist penetration by the light density coal particles, orthey may be recirculated in similar apparatus. This does not remove thenecessity for the heavy density fluid process treatment but reduces thequantity of coal escaping with the rejects, and may reduce the number ofdraws from which particles should be retreated by the heavy densityfluid process.

The preferred embodiment of the invention is illustrated in theaccompanying drawings in which Fig. 1 isv a side view of my separatingapparatus; Fig. 2 is a transverse vertical section through one of theexhauster hoods; Fig. 3 is an enlarged vertical section takenapproximately on the line III-III of Fig. 1 but including the centraleccentrics that oscillate the tables; .Fig. 4 is an enlarged view of thegate-operating mechanism taken on the line IV--IV of Fig. 3; Fig. 5 isan enlarged side view, partly in section, of one of the separatingtables; Fig. 6 is a graph showing terminal velocities of particles ofcertain sizes and densities in air; and Fig. '7 is a graph showingapproximate air volumes required to develop mobility of beds of coalparticles of different sizes.

Referring to Fig. 1 of the drawings, four upright corner posts I arerigidly connected at their tops and bottoms by inclined structuralmembers 2 and 3, respectively. The rigid framework thus formed rests ona substructure 4 and supports the cleaning apparatus now to bedescribed. I

Suspended from top members 2 by means of multiple leaf springs 5 is apair of inclined frames 6 having open central potrions. Rigidly securedto a bracket 1 depending from each side of each frame is one end of aleaf spring 8, the other end of which is attached to one end of aconnecting rod 9. The other end of the connecting rod is connected to aneccentric ll mounted on a shaft I2 journaled in bearings 43 fastened tobottom framework members 3 (Figs. 1 and 3). This shaft is driven througha fly-wheel pulley M by any suitable means, and through the eccentricsand connecting rods it causes the two frames to reciprocate oroscillate. Eccentrics H are mounted 180 apart so that they move theframes toward and away from each other at the same rates ofacceleration, whereby vibration in the framework is held at a minimum.

Mounted on frames 6 are a plurality of tables 15, I6, [1, I8, l9 and 20,each of which is slightly below the preceding one so that particles canflow from the discharge end of each table through a spout 2| to theupper end of the next table. Each table is more or less box-like with anopen top and with the upper half of a hinge 22 attached to its frontwall. The lower half of the hinge is connected to the front wall of abox 23 mounted in the underlying frame and having an open top andbottom. The rear end of the table is supported by means of upright bolts24 pivotally connected to the top of the supporting frame 6 andextending up through brackets 26 attached to the sides of the table.Nuts 2'! determine the position of the brackets vertically of the bolts,while a bellows-type of coupling 28 seals the space between table andbox regardless of the adjustments of the nuts.

About half-way down in each table there is a foraminous deck 3| themajor portion of which is fiat and unobstructed and inclined downwardlyfrom the feed end of the table. Near the lower or discharge end of thetable the deck is provided with a discharge opening or draw 32, as shownin Fig. 5, between which and the adjacent end of the table the deck isinclined upwardly a slight amount. The draw is connected by conduitsections 33 and 34 and flexible coupling 36 with a casing 31 rigidlysuspended from the frame (Figs. 1 and 3). The bottom of this casingslopes laterally and terminates in a spout 38 which empties intoanysuitable conveyor (not shown) disposed at one side of the machine, or

ends of the gate and mounted in bearings 42 attached to the frame 6above. The gate is rotated back and forth by means of a lever 43 (Figs.3 and 4) extending laterally from one of the stub shafts 4| and providedwith a longitudinal slot 44. A pin 46 is loosely mounted in this slotand is carried by a slide 41 disposed in a radial slot 48 in a disc 49where it is adjustable by a threaded rod 5|. The disc is rotated by anelectric motor 52 mounted on one of the lower framework members 3. Asthe disc rotates, the lever arm and curved gate are oscillated and thedischarge of particles from the draw thereby effected. Discharge isfacilitated by a 'bar 53 mounted in fixed position between the bottom ofconduit 34 and the gate. The rate of discharge is determined by the rateand amplitude of oscillation of the gate. .The rate of oscillation isdetermined by the speed of revolving disc 49, and the amplitude by theposition of pin 46 relative to the center of the disc.

The hollow space in each table below its pervious deck is divided into aplurality of compartments by transverse partition members 56 disposed atspaced intervals longitudinally of the table, as shown in Fig. 5. At thebottom of these compartments there is a floor 51 provided beneath eachcompartment with a series of openings 58 (Fig. 3). Between thecompartments the floor is provided with parallel depending ribs 59carrying laterally projecting flange members 6| that supportlongitudinally slidable valve plates 62. Each of these plates isprovided with a series of openings 63 adaptedto register with openings58 when the plate is in one position, and to overlap the solid portionsof the floor when in any other position whereby the volume of airentering each compartment can be independently regulated. Adjustment ofeach valve plate is effected by means of a screw 64 threaded in a block66 attached to the bottom of the valve plate, the outer end of the screwbeing journaled in fixed position in a plate 61 secured to the outsideof the table.

Air is supplied to the tables through ducts 68 extending downwardly fromboxes 23 and connected by flexible couplings 69 to stationary verticalducts 'H communicating with a main horizontal duct 12. ably a main valve13 for providing coarse regulation of the air supplied to the tables. Itwill be seen in Fig. 5 that draw 32 has an offset portion and that thereis therefore a short compartment 14 below the deck opening. This is forthe purpose of permitting air to be forced upwardly through the deckopening as well as through the remainder of the deck. To further preventany material portion of the deck from being unexposed to the upward aircurrents, the upper edges of partition members 56 are tapered.

As the upward air streams will of course carry some dust particles upwith them from the tables, I an exhaust hood 8| is suspended in anysuitable manner over each table. These hoods are all In each duct Hthere is prefer connected to a common duct in which there is an exhaustfan (not shown). Each hood is preferably provided with a main valve 82for roughly adjusting the suction therethrough. As shown in'Fig. 2, eachhood is rectangular when viewed transversely of 'the'table, and isprovided near its lower end with a perforated plate 83 that ofiersresistance to the air current entering the hood. With this constructionthe upward velocity of the air entering the hood is maintainedsubstantially uniform across its width, instead of being so decreasednear its sides as to permit dust-laden air to escape therefrom. Eachhood is also preferably provided with a plate 84 having several parallelrows of openings therethrough which are regulated in size by underlyingindependently adjustable valve plates 86. This valve structure issubstantially the same as that used in the tables, although the endopenings 81 in the valves are larger than the others to aid inincreasing the air velocity at the sides of the hood. The purpose ofthese valves is to permit the suction by each hood to be maintainedsubstantially uniform lengthwise of the underlying table by decreasingit at the central portion of the hood.

In practicing my invention with the apparatus disclosed herein the rawcoal, or other particulate material to be separated, is first presizedby screening or the like in order to obtain a size range in which all ofthe foreign particles to be removed have terminal velocities greaterthan the upward fluid velocity through the lightest density or pure coalbed in the mixture required to develop mobility of that bed. Although itis the general practice to screen raw coal to divide it into differentgrades or size ranges for classification purposes, these ranges bear noparticular relation to the fluid velocities required in cleaning themixture. As an example of the application of my invention, assume thatraw coal, that has thus been roughly sized so that the smallestparticles in the mixture are .1 inch in diameter, is to be cleaned. Inaccordance with this invention the largest size or coarsest particlesthat can be included in the feed to the separating apparatus must bedetermined in order to find the size range of the raw coal particlesthat can be cleaned satisfactorily. By reference to the graph shown inFig. 6 it will be seen that a foreign particle of .1 inch diameter andof 1.75 density, which is bone coal, has a terminal velocity in air ofabout 1700 feet per minute. or course, the foreign particles of greaterdensities have greater terminal velocities. The solid diagonal line inthe graph of Fig. 7 illustrates the approximate upward air velocitythrough a bed of pure coal of average shape (approximately 1.30 density)necessary to develop mobility of that bed in which the coarsestparticles are of any given size. In order that the smallest and lightestforeign particles which it is desired to remove may settle through thisupward air current, its velocity must be less than the terminal velocityof those particles; in this example 1700 feet per minute for thesmallest bone coal particles. To cause quick stratification or rapidsettling of the bone coal when the mixture reaches the last deck, theupward air velocity at that deck might be limited to 1500 or 1600 feetper minute. The Fig. 7 graph shows that with such air velocity thecoarsest particles of pure coal that can be in the feed and stillpersize range is restricted to raw coal particles having a minimumdiameter of substantially .1 inch and a maximum diameter ofsubstantially .475 inch. The raw coal should therefore be presized byscreening to obtain this size range. By taking a1475 inch particle onthe dotted diagonal line in Fig. 7, the approximate number of cubic feetof air required per minute for each square foot of deck space can befound at the right side of the graph.

As previously pointed out, it is very difficult to separate particlesvarying only slightly in density, although it can be done with more orless success if the size range is small, the ideal condition being onein which all particles are of substantially the same size. Therefore, ifit is desired to have coal exceptionally free from lighter density bonecoal (thelightest density foreign matter) it is advisable to use a sizerange smaller than the maximum one in which all of the foreign particleshave terminal velocities greater than the upward air velocity requiredto develop mobility of the coal bed.

If it is not desired to remove bone coal, but only foreign particles ofa density of about 2.00 and greater, the Fig. 6 graph shows that theterminal velocity of particles of 2.00 density and .1 inch diameter isabout 1850 feet per minute. Taking an upward air velocity of 1700 feetto allow for rapid Stratification, Fig. 7 shows that in order to developmobility of the coal bed the coarsest particles in the feed should notbe over about .5 inch in diameter, and that approximately 550 cubic feetof air per minute per square foot of deck space should be supplied tothe last deck.

Conversely, if raw coal has been previously rough-sized so that itslargest particles are .6 inch in diameter, it is found in Fig. 7 that itwill take an upward air velocity through the mixture of about 2100 feetper minute to develop mobility of the coal bed. According to thisinvention, all of the foreign particles that it is desired to removefrom the mixture must therefore have terminal velocities in excess of2100 feet per minute. By reference to Fig. 6 it will be seen that bonecoal particles (density of the order of 1.75) of .15 inch diameter orslightly smaller will settle, as will all of the heavier densityparticles of that size. The proper maximum size range is thussubstantially .15 inch by .6 inch.

Although the graphs of Figs. 6 and 7 chart particle sizes up to 1 inchin diameter, due to the cost of the great volume of air required todevelop mobility of a coal bed comprising particles of such large size,this method of cleaning coal is not recommended for particles over A ofan inch in diameter.

The pitch of the first deck is so adjusted by nuts 2'! in connectionwith the rate of feed and the oscillations of gate 39 that the heavydensity particles travel towards the draw at about the same rate theyare withdrawn therefrom, whereby the depth of the heavy density bed ismaintained substantially constant. This bed is so dense that it preventsthe intermediate and light density particles from penetrating it. As itis only necessary to remove the coarser heavier density foreignparticles from the first deck, the upward air Velocity through themixture thereon may be increased so that the fine particles can notsettle through it.

The maximum depth of the heavy density bed is determined by a barrierplate 9| (Fig. 5) extending transversely of the deck at its dischargeend. To assist in regulating the total depth of the mixture on the deck,the velocity of flow of particles through spout 2| is regulated. This isdone by providing the spout floor with a per- 'forated section 96 upthrough which air is blown from a compartment 9'! below the spoutprovided with a regulating valve plate 98. The feed, deck pitch andwithdrawal are so regulated that the heavy density bed does not flowover barrier 91 onto the second deck. It has been found that if abarrier alone is provided close to the draw the particles between it andthe draw tend to circulate in vertical planes, whereby lighter densityparticles are drawn into the lower strata. Consequently, the heavierdensity particles cannot be removed through the draw without includingsome of thelighterdensity particles. To aid in reducing this circulation a plurality of vertical baffle plates 82 extending longitudinallyof the deck are preferably mounted on edge directly in front of thebarrier at transversely spaced intervals across the deck. The frictiondeveloped between the heavy density particles and the sides of thesebailles materially decreases their circulation, and the portion of thebed between the draw and barrier 9| forms a body in the nature of ashock-absorber which does not permit circulation still existing atbarrier 9! to extend across the intervening space to the draw and takeplace at the point where the freely moving particles are removed throughthe draw. The two air compartments between the barrier and draw areprovided for the two-fold purpose of developing the fluidity required inthe heavier density bed at the draw to permit flow into the draw withoutvertical circulation, and, in combination with rifiles 92 and barrierSI, of gradually reducing the fluidity over the two compartments to adegree of comparative compactness at barrier 9|.

As there is always a reservoir of heavy density particles over the draw,and as the particles that are withdrawn from this bed are taken from thebottom of this reservoir, it can safely be said that nothing but heavydensity particles or rejects are withdrawn through the first draw. Thelight density particles or coal, and the intermediate density particles,except possibly the coarsest, together with some of the very smallestparticles of heavier density, flow from the first deck over barrier 9|and through spout 2! to the second deck in table IS.

The physical characteristics of the raw coal mixture on' the second deckare difierent from those of the raw coal on the first deck because mostof the heaviest density and coarse intermediate density foreignparticles have been removed. Because of this the terminal velocities ofthe heavy density particles remaining in the second bed are lower, sothe upward fluid velocity through the mixture on the second deck shouldbe reduced, but suflicient velocity must still be maintained to keep thebed of pure coal mobile in order to develop the condition of fluidityrequired for satisfactory Stratification. The finer heavy densityparticles are Stratified in the lower stratum of the heavy density bedaccumulating on this second deck, together with such intermediate andlighter density particles both. Therefore, to effect an accumulation ofa heavy density bed on the second deck, it is necessary to adjust thepitch of the deck surface to that required. Since the heavy density bedon the second deck necessarily includes particles whose average densityis less than the average density of those accumulated on the first deck,and as it is likewise more mobile under the combined influence ofmechanical agitation and the upward fluid stream, its resistancetopenetration by intermediate density and some lighter density particlesis less pronounced.

Each successive deck is adjusted in pitch and air stream to produce thenecessary stratification and accumulation of the heavier of theremaining particles in a heavy density bed thereon. As the heavy densitybed is lighter in average density on each succeeding deck, a point isreached in the passage of raw coal from deck to deck Where a smallamount of the lighter intermediate density particles and certain of thelight density particles may penetrate the heavy density bed and bewithdrawn with the rejects. However, on each succeeding deck the entiremixture contains fewer intermediate density particles and fewer, if any,of the extremely fine heavy density particles.

On the last deck the terminal velocities of the heavier and intermediatedensity particles are still greater thanthe minimum air velocityrequired to keep the pure coal bed mobile. Nevertheless, as theseparticles are so much smaller, their average density is so close to theaverage density of the coal particles that they tend to associate inSettling with some of the coal particles which have approximately thesame terminal velocities. It is therefore probably inevitable that somecoal will be withdrawn with the rejects from the last deck or the lastseveral decks, depending upon the density of the lightest particlesrequired to be removed. The rejects from the last deck may berecirculated through the entire apparatus in order to. produce lowerstrata of greater density on the 'various decks, and this will to someextent increase resistance to penetration by coal particles. Or, anydesired amount of the rejects may be retreatedalone by ahindered-crowded settling process in similar apparatus.

To effect complete separation of coal from the finest of the lightestdensity rejects it is highly desirable to subject the rejects from oneor more draws preceding the last draw to a heavy density fluid processin which size and shape have no influence. Such a process is one inwhicha heavy density fluid, such as calcium chloride or other chemical,or the equivalent in a mixture of sand and water, is employed at thegravity required to effect the desired separation of the light densityparticles from the heavier density particles. In some cases it may befound desirable to screen the rejects before retreatment in order toremove the finest sizes without sub-.

mitting them to such retreatment.

Heretofore the separation of particle sizes below A; inch square meshhas been extremely difiicult and usually impracticable. Such separationscan be produced satisfactorily with my method and apparatus if theparticles fed to the presizing apparatus are extremely dry. But with theaverage conditions usually encountered in practice excessive moisture ispresent on the surface of the fines below A inch to A; inch. Thismoisture holds fine dust particles below 35 or 48 mesh against thecoarser particles, whereby the mixture is not susceptible to thedevelopment of the fluid conditions required for effectivestratification. I have found that in order to separate particles below/8 inch ordinarily, and in many cases below /4 inch, it is advisable toreduce this extraneous moisture to a maximum of about 2 per cent to 3per cent by weight and to remove extremely fine dust particles below 35to 48 mesh. After the moisture and dust particles have been removed, theremaining particles can then be sized in accordance with the presentinvention and fed to the separating apparatus described herein.

According to the provisions of the patent statutes, I have explained theprinciple and mode of practicing my invention and have illustrated anddescribed what I now consider to represent its best embodiments.However, I desire to have it understood that, within the scope of theappended claims, the invention may be practiced otherwise than asspecifically illustrated and described.

I claim:

1. Apparatus for cleaning particulate material, comprising a series'oflongitudinally inclined flat foraminous decks, each provided with abottom draw adjacent to but spaced from its lower end, the short deckportion between said draw and lower end lying in a plane intersectingthe plane of the main portion of the deck at an obtuse angle, meansmounted on said short deck portion for retarding movement of the lowerbed of particulate matter thereon, a barrier member extendingtransversely of the delivery end of said short deck portion, a rigidlymounted elevated frame, a rigid frame disposed below said elevated frameand movably suspended therefrom, means on. said suspended frameconnected with said decks for independently adjusting the pitch of eachdeck, means for actuating said suspended frame to reciprocate the deckslongitudinally, and means for directing fluid under pressure upwardlythrough the decks and draws.

2. Apparatus for cleaning particulate material, comprising a series oflongitudinally inclined flat foraminous decks, each provided with abottom draw adjacent to but spaced from its lower end, there being afiat short deck portion between said draw and lower end lying in a planeintersecting the plane of the main portion of the deck at an obtuseangle, a rigidly mounted elevated frame, a rigid frame disposed belowsaid elevated frame and movably suspended therefrom, means on saidsuspended frame connected with said decks for independently adjustingthe pitch of each deck, means for actuating said suspended frame toreciprocate the decks longitudinally, a plurality of upright partitionsforming open-top compartments directly below each deck and draw andextending transversely thereof, the top of each partition being taperedupwardly to reduce its thickness, means for directing fluid underpressure to said compartments, and means for independently controllingthe supply of fluid to each compartment.

3. Apparatus for cleaning particulate material, comprising a series oflongitudinally inclined foraminous decks, each provided with a bottomdraw adjacent to but spaced from its lower end, means for independentlyadjusting the pitch of each deck, means for reciprocating the deckslongitudinally, means for directing fluid under pressure upwardlythrough the decks, an exhaust hood mounted above and spaced from eachdeck for receiving said fluid, each hood tion transversely of the deck,a plate provided with rows of openings disposed in said hood andextending therein across the lower intake portion thereof, the openingsnear the periphery of said plate being larger than the openings in thecentral portion thereof to increase the air velocity at the sides ofsaid hood, and a substantially rectangular exhaust duct connected to thetop of said hood and being substantially as wide as the hood, wherebyuniform air velocities are obtained in said hood.

4. Apparatus for cleaning particulate material, comprising a series oflongitudinally inclined foraminous decks, each provided with a bottomdraw adjacent to but spaced from its lower end, means for independentlyadjusting the pitch of each deck, means for reciprocating the deckslongitudinally, means for directing fluid under pressure upwardlythrough the decks, a substantially rectangular exhaust hood mountedabove each deck for receiving said fluid, a substantially rectangularexhaust deck connected to the top of said hood and being substantiallyas wide as the hood, and a plurality of substantially parallel valvemembers mounted in each hood and extending transversely thereof, eachmember being provided with a series of adjustable valve openings.

5. Apparatus for cleaning particulate material, comprising a series oflongitudinally inclined flat foraminous decks, a spout connected to thelower end of each deck and emptying onto the next succeeding deck, eachdeck being provided with a bottom draw adjacent to but spaced from itslower end, a rigid elevated mounting frame, a rigid frame disposed belowsaid elevated frame and movably suspended therefrom, means on saidsuspended frame connected with said decks for independently adjustingthe pitch of each deck, means for actuating said suspended frame toreciprocate the decks longitudinally, means for directing fluid underpressure upwardly through the decks, and means for directing fluid underpressure upwardly through the bottom of said spout for regulating thedepth of the upper bed of particles on the adjoining deck.

6. Apparatus for cleaning particulate material, comprising a rigidelevated structural frame, a mounting frame disposed below said elevatedframe and extending substantially in parallel therewith, spring meansfor suspending said mounting frame from said structural frame, means forreciprocating said mounting frame longitudinally, a plurality of boxesrigidly mounted in said mounting frame and having open tops and bottoms,conduits flexibly connected to the bottoms of the boxes for deliveringfluid thereto, a box-like table disposed above each of said boxes, ahinge connecting one end of each table to its underlying box, meanshingedly attached to said mounting frame and adjustably connected withthe opposite end of each table for raising and lowering said oppositeend of each table independently of the other tables, flexible couplingsconnecting each table and its supporting box, a longitudinally inclinedflat foraminous deck in the upper portion of each table, each deck beingprovided with a bottom draw adjacent to but spaced from its lower end, adischarge conduit leading downwardly from said draw, a plurality ofupright partition members extending transversely of each deck to dividethe table below the deck into a plurality of being substantiallyrectangular in vertical sec- 7 longitudinally spaced fluid compartments,and a separate valve at the lower end of each compartment.

'7. Apparatus for cleaning particulate material, comprising a series oflongitudinally inclined foraminous decks, each provided with a bottomdraw adjacent to but spaced from its lower end, means for independentlyadjusting the pitch of each deck, means for reciprocating the deckslongitudinally, means for directing fluid under pressure upwardlythrough the decks, a substantially rectangular exhaust hood mountedabove each deck for receiving said fluid, a substantially rectangularexhaust duct connected to the top of said hood and being substantiallyas wide as the hood, a plurality of substantially parallel valve membersmounted in each hood and extending transversely thereof, each memberbeing provided with a series of adjustable valve openings, and aforaminous member disposed below said valve members and extending acrossthe entire width and length of the hood.

8. Apparatus for separating particulate material in accordance with thespecific gravities of the particles thereof comprising, in combination,means forming a rigid longitudinally inclined centrally open top frame,yieldable means depending from the sides of said top frame, a pluralityof structural members secured to the lower ends of said yieldable meanson either side of said top frame and forming below the top frame aplurality of centrally open mounting frames which are yieldablysuspended from said top frame by said yieldable means and extendtherebelow substantially in parallel therewith but lengthwise spacedfrom each other, a plurality of structures each individually adjustablymounted on each of said mounting frames forming between the sides ofsaid inclined top frame a descending series of individual separatingtables, each table comprising sides forming a a box-like frame open atthe top, a perforate longitudinally inclined deck disposed in saidboxlike frame below the upper edges of the sides thereof for receivingmaterial to be separated, each deck provided with a bottom draw adjacentto but spaced from its lower end, a discharge spout for each deckdisposed at the lower end thereof above the adjacent upper endof thenext lower table for delivering separated material to the deck of saidnext lower table, means forming air compartments extending transverselyunderneath and across the entire deck and underneath and across saiddischarge spout, means for directing air under pressure to saidcompartments for agitating the material thereon, and actuating means forperiodically moving said suspended mounting frames simultaneouslylongitudinally toward and away from each other at substantially the samerates of acceleration to reciprocate said tables, whereby the vibrationof the entire apparatus structure is held at a minimum.

9. The structure and combination defined in claim 8, together with anexhaust hood for each deck disposed thereabove but spaced therefrom forreceiving the air directed tosaid compartments and through the materialon the deck, and

means in said exhaust hood for maintaining uniform air velocitiestherein across the lower end thereof which is disposed above said deck.

10. The structure and combination defined in claim 8, together with anexhaust hood for each means for controlling the flow of air through saidopenings, and a perforate plate in said hood spaced from said valvemeans, whereby uniform air velocities are obtained in said hood.

MACK E. HAWORTI-I.

